Semiconductor device and method of fabricating the same

ABSTRACT

According to one aspect of the invention, there is provided a semiconductor device fabrication method comprising: forming a first gate electrode via a first gate insulating film on a P-type semiconductor region formed in a surface portion of a semiconductor substrate, and forming a second gate electrode via a second gate insulating film on an N-type semiconductor region formed in the surface portion of the semiconductor substrate; forming a first insulating film on side surfaces of the first gate electrode and the first gate insulating film, and forming a second insulating film on side surfaces of the second gate electrode and the second gate insulating film; forming a mask having a pattern corresponding to the P-type semiconductor region; etching away the second insulating film by using the mask; removing the mask; and forming a first gate electrode sidewall insulating film on the side surfaces of the first insulating film, and forming a second gate electrode sidewall insulating film on the side surfaces of the second gate electrode and the second gate insulating film, thereby forming an interface insulating film in an interface between the second gate electrode and the second gate insulating film.

CROSS REFERENCE TO RELATED APPLICATION

This application is based upon and claims benefit of priority under 35USC §119 from the Japanese Patent Application No. 2005-281537, filed onSep. 28, 2005, the entire contents of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

The present invention relates to a semiconductor device and a method offabricating the same.

Recently, the film thickness of a gate insulating film decreases asdownsizing of MOSFETs advances, and this poses the problem that a gateleakage current increases. To suppress this gate leakage current,therefore, it is proposed to use a high-k film having a relativedielectric constant higher than that of a silicon oxide (SiO₂) film as agate insulating film. An example of this high-k film is a hafniumsilicate nitride (HfSiON) film.

When a complementary MOS transistor (to be referred to as a CMOSFEThereinafter) including a PMOSFET and NMOSFET is to be formed, however,if this hafnium silicate nitride (HfSiON) film is used as a gateinsulating film, the gate threshold voltage of the PMOSFET fluctuatesmore than that of the NMOSFET.

In this case, a driving current flowing through a channel region reducesmore in the PMOSFET than in the NMOSFET, so the drivability of thePMOSFET decreases. This produces a large difference in drivabilitybetween the PMOSFET and NMOSFET.

A reference related to a CMOSFET using a high-k gate insulating film isas follows.

Japanese Patent Laid-Open No. 2004-289061

SUMMARY OF THE INVENTION

According to one aspect of the invention, there is provided asemiconductor device fabrication method comprising:

forming a first gate electrode via a first gate insulating film on aP-type semiconductor region formed in a surface portion of asemiconductor substrate, and forming a second gate electrode via asecond gate insulating film on an N-type semiconductor region formed inthe surface portion of the semiconductor substrate;

forming a first insulating film on side surfaces of the first gateelectrode and the first gate insulating film, and forming a secondinsulating film on side surfaces of the second gate electrode and thesecond gate insulating film;

forming a mask having a pattern corresponding to the P-typesemiconductor region;

etching away the second insulating film by using the mask;

removing the mask; and

forming a first gate electrode sidewall insulating film on the sidesurfaces of the first insulating film, and forming a second gateelectrode sidewall insulating film on the side surfaces of the secondgate electrode and the second gate insulating film, thereby forming aninterface insulating film in an interface between the second gateelectrode and the second gate insulating film.

According to one aspect of the invention, there is provided asemiconductor device comprising:

a first gate insulating film formed on a P-type semiconductor region ina surface portion of a semiconductor substrate;

a first gate electrode formed on said first gate insulating film;

a first gate electrode sidewall insulating film formed on side surfacesof said first gate electrode and said first gate insulating film via aninsulating film;

an N-channel transistor having a first source region and a first drainregion formed on two sides of a first channel region formed in a surfaceportion of said P-type semiconductor region below said first gateelectrode;

a second gate insulating film formed on an N-type semiconductor regionin the surface portion of said semiconductor substrate;

a second gate electrode formed on said second gate insulating film viaan interface insulating film;

a second gate electrode sidewall insulating film formed on side surfacesof said second gate electrode, said interface insulating film, and saidsecond gate insulating film; and

a P-channel transistor having a second source region and a second drainregion formed on two sides of a second channel region formed in asurface portion of said N-type semiconductor region below said secondgate electrode.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal sectional view showing an element sectionalstructure in a predetermined step of a method of fabricating a CMOSFETaccording to an embodiment of the present invention;

FIG. 2 is a longitudinal sectional view showing an element sectionalstructure in a predetermined step of a method of fabricating theCMOSFET;

FIG. 3 is a longitudinal sectional view showing an element sectionalstructure in a predetermined step of a method of fabricating theCMOSFET;

FIG. 4 is a longitudinal sectional view showing an element sectionalstructure in a predetermined step of a method of fabricating theCMOSFET;

FIG. 5 is a longitudinal sectional view showing an element sectionalstructure in a predetermined step of a method of fabricating theCMOSFET;

FIG. 6 is a longitudinal sectional view showing an element sectionalstructure in a predetermined step of a method of fabricating theCMOSFET;

FIG. 7 is a longitudinal sectional view showing an element sectionalstructure in a predetermined step of a method of fabricating theCMOSFET;

FIG. 8 is a longitudinal sectional view showing an element sectionalstructure in a predetermined step of a method of fabricating theCMOSFET;

FIG. 9 is a longitudinal sectional view showing an element sectionalstructure in a predetermined step of a method of fabricating theCMOSFET;

FIG. 10 is a longitudinal sectional view showing an element sectionalstructure in a predetermined step of a method of fabricating theCMOSFET;

FIG. 11 is a graph showing the current-voltage characteristics of anNMOSFET and PMOSFET forming the CMOSFET; and

FIG. 12 is a graph showing the current-voltage characteristics of anNMOSFET and PMOSFET forming the CMOSFET.

DETAILED DESCRIPTION OF THE INVENTION

An embodiment of the present invention will be described below withreference to the accompanying drawings.

FIGS. 1 to 10 illustrate a method of fabricating a CMOSFET according toan embodiment of the present invention. First, a resist mask having adesired pattern is formed on a semiconductor substrate 10 byphotolithography, and used as a mask to ion-implant boron (B), gallium(G), indium (In), or the like.

Similarly, a resist mask having a desired pattern is formed on thesemiconductor substrate 10, and used as a mask to ion-implant phosphorus(P), arsenic (As), antimony (Sb), or the like. Annealing is thenperformed to form a P-type semiconductor region 20 and N-typesemiconductor region 30 as shown in FIG. 1. Subsequently, as shown inFIG. 2, an element isolation insulating film 40 is formed in a desiredregion on the semiconductor substrate 10.

After that, an insulating film made of, e.g., a hafnium silicate nitride(HfSiON) film is formed on the surface of the semiconductor substrate10. Note that this insulating film is not limited to the hafniumsilicate nitride film. That is, it is possible to use various types ofhigh-k films having relative dielectric constants higher than that of asilicon oxide (SiO₂) film. Examples are a hafnium oxide (HfOx) film, azirconium oxide (ZrOx) film, a silicate film of a hafnium oxide film, analuminate film of a hafnium oxide film, a silicate film of a zirconiumoxide film, an aluminate film of a zirconium oxide film, a silicatenitride film of a hafnium oxide film, an aluminate nitride film of ahafnium oxide film, a silicate nitride film of a zirconium oxide film,and an aluminate nitride film of a zirconium oxide film.

Polysilicon is deposited on this insulating film by CVD or the like toform a polysilicon film. In this case, a polysilicon germanium film mayalso be formed by depositing polysilicon germanium on the insulatingfilm.

As shown in FIG. 3, the polysilicon film and hafnium silicate nitride(HfSiON) film are sequentially patterned by lithography and RIE, therebyforming a gate electrode 70 and gate insulating film 50 on the P-typesemiconductor region 20, and a gate electrode 80 and gate insulatingfilm 60 on the N-type semiconductor region 30.

As shown in FIG. 4, a silicon nitride (SiN) film 90 about 2 nm thick isformed on the entire surface. As shown in FIG. 5, the silicon nitride(SiN) film 90 is removed by RIE except for the silicon nitride (SiN)film 90 formed on the side surfaces of the gate electrode 70 and gateinsulating film 50, and on the side surfaces of the gate electrode 80and gate insulating film 60. In this manner, offset spacers 100A and100B are formed on the side surfaces of the gate electrode 70 and gateinsulating film 50, and offset spacers 110A and 110B are formed on theside surfaces of the gate electrode 80 and gate insulating film 60.

As shown in FIG. 6, an N-type dopant such as phosphorus (P) ision-implanted into the P-type semiconductor region 20, and annealing isso performed as to diffuse this phosphorus (P), thereby forming ashallow-junction, lightly doped source extension region 120A and drainextension region 120B.

Also, a P-type dopant such as boron (B) is ion-implanted into the N-typesemiconductor region 30, and annealing is so performed as to diffusethis boron (B), thereby forming a shallow-junction, lightly doped sourceextension region 130A and drain extension region 130B.

As shown in FIG. 7, the semiconductor substrate 10, gate electrodes 70and 80, and offset spacers 100 and 110 are coated with a photoresist,and the photoresist is exposed and developed to form a resist mask 140having a pattern which opens over the N-type semiconductor region 30,thereby covering the P-type semiconductor region 20 with the resist mask140.

The resist mask 140 is used as a mask to etch away the offset spacers110A and 110B formed in the N-type semiconductor region 30.

Note that wet etching using hydrofluoric acid (HF) may also be performedinstead of RIE. In this case, the offset spacers 110A and 110B may alsobe removed after they are changed into an oxynitride film or oxide filmby radical oxidation or thermal oxidation. Alternatively, the sourceextension region 130A and drain extension region 130B may also be formedafter the offset spacers 110A and 110B are removed.

As shown in FIG. 8, after the resist mask 90 is removed, a silicon oxide(SiO₂) film made of, e.g., a TEOS (tetraethoxysilane) film is formed onthe entire surface of the semiconductor substrate 10. As shown in FIG.9, this silicon oxide (SiO₂) film is etched by RIE to form gateelectrode side walls 150A and 150B on the side surfaces of the offsetspacers 100A and 100B, and gate electrode side walls 160A and 160B onthe side surfaces of the gate electrode 80 and gate insulating film 60.

In this state, the gate electrode side walls 160A and 160B act on theinterface between the gate electrode 80 and gate insulating film 60formed on the N-type semiconductor region 30, thereby forming a low-kinterface insulating film (interface layer) 170 made of a silicon oxide(SiO₂) film about 2 to 3 nm thick in the interface between the gateelectrode 80 and gate insulating film 60.

On the other hand, the offset spacers 100A and 100B are already formedon the side surfaces of the gate electrode 70 and gate insulating film50 formed on the P-type semiconductor region 20. Therefore, even whenthe gate electrode side walls 150A and 150B are formed, they do not acton the interface between the gate electrode 70 and gate insulating film50, so almost no interface insulating film forms.

Although a silicon oxide film made of a TEOS film is used as the gateelectrode side walls 150 and 160 in this embodiment, it is also possibleto use any of various silicon oxide films such as HTO (High TemperatureOxide), BPSG (Borophosphosilicate Glass), PSG (Phosphosilicate Glass),and BSG (Boron-Silicate Glass).

As shown in FIG. 10, an N-type dopant such as phosphorus (P) ision-implanted into the P-type semiconductor region 20, and annealing isso performed as to diffuse this phosphorus (P), thereby forming a sourceregion 180A and drain region 180B.

Also, a P-type dopant such as boron (B) is ion-implanted into the N-typesemiconductor region 30, and annealing is so performed as to diffusethis boron (B), thereby forming a source region 190A and drain region190B.

After a metal film made of, e.g., cobalt (Co), nickel (Ni), or platinum(Pt) is formed by sputtering, annealing is performed to form suicides200A to 200C for reducing the parasitic resistance on the surface of thegate electrode 70 and in the surface portions of the source region 180Aand drain region 180B, and form silicides 210A to 210C on the surface ofthe gate electrode 80 and in the surface portions of the source region190A and drain region 190B.

Subsequently, an interlayer dielectric film (not shown) is formed, and awiring step is performed by forming contact plugs (not shown) in thisinterlayer dielectric film, thereby forming a CMOSFET 240 including anNMOSFET 220 and PMOSFET 230.

In the CMOSFET 240 fabricated by the above method, as shown in FIG. 10,the element isolation insulating film 40 is formed in the surfaceportion of the semiconductor substrate 10. Near the central portion ofthe P-type semiconductor region 20 isolated by the element isolationinsulating film 40, the gate electrode 70 is formed via the gateinsulating film 50 formed on the surface of the semiconductor substrate10.

The gate electrode side walls 150A and 150B are formed on the sidesurfaces of the gate electrode 70 and gate insulating film 50 via theoffset spacers 100A and 100B about 2 nm thick. Also, a channel region250 is formed near the surface of the semiconductor substrate 10 belowthe gate electrode 70.

The source extension region 120A and drain extension region 120B areformed on the two ends of the channel region 250.

The source region 180A is formed between the source extension region120A and an element isolation insulating film (not shown). The drainregion 180B is formed between the drain extension region 120B andelement isolation insulating film 40.

In addition, the suicides 200A to 200C for reducing the parasiticresistance are formed on the surface of the gate electrode 70 and on thesurfaces of the source region 180A and drain region 180B.

On the other hand, the gate electrode 80 is formed near the centralportion of the N-type semiconductor region 30 via the gate insulatingfilm 60 formed on the surface of the semiconductor substrate 10, and theinterface insulating film 170 made of a silicon oxide (SiO₂) film about2 to 3 nm thick.

The gate electrode side walls 160A and 160B are formed on the sidesurfaces of the gate electrode 80, interface insulating film 170, andgate insulating film 60. Also, a channel region 260 is formed near thesurface of the semiconductor substrate 10 below the gate electrode 80.

The source extension region 130A and drain extension region 130B areformed on the two ends of the channel region 260.

The source region 190A is formed between the source extension region130A and element isolation insulating film 40. The drain region 190B isformed between the drain extension region 130B and an element isolationinsulating film (not shown).

In addition, the suicides 210A to 210C for reducing the parasiticresistance are formed on the surface of the gate electrode 80 and on thesurfaces of the source region 190A and drain region 190B.

FIGS. 11 and 12 illustrate the current-voltage characteristics of theNMOSFET and PMOSFET forming the CMOSFET. In each of FIGS. 11 and 12, theabscissa indicates the gate voltage applied to the gate electrode, andthe ordinate indicates the drain current (the driving current flowingthrough the channel region).

As shown in FIG. 11, when a hafnium silicate nitride (HfSiON) film isused as the gate insulating film, the gate threshold voltage of thePMOSFET changes by about 0.6 V in the negative direction, but that ofthe NMOSFET changes only by about 0.2 V in the positive direction,compared to the case in which a silicon oxide (SiO₂) film is used as thegate insulating film.

As described above, the driving current flowing through the channelregion reduces more in the PMOSFET than in the NMOSFET, so thedrivability of the PMOSFET decreases. This produces a large differencein drivability between the PMOSFET and NMOSFET.

In this embodiment, therefore, the offset spacers 100A and 100B areformed on the side surfaces of the gate electrode 70 and gate insulatingfilm 50 only in the NMOSFET 220, and no offset spacers are formed in thePMOSFET 230, thereby forming the interface insulating film 170 in theinterface between the gate electrode 80 and gate insulating film 60 inthe PMOSFET 230.

Negative fixed electric charge is generated in the interface insulatingfilm 170. When the interface insulating film 170 is formed, therefore,the gate threshold voltage of the PMOSFET 230 changes by about 0.16 V inthe positive direction (FIG. 12), compared to the case in which nointerface insulating film is formed.

As described above, when the interface insulating film 170 is formed,the driving current largely increases, and this improves the drivabilityof the PMOSFET 230, compared to the case in which no interfaceinsulating film is formed. Consequently, the difference in drivabilitybetween the NMOSFET 220 and PMOSFET 230 can be reduced.

Accordingly, the semiconductor device and the method of fabricating thesame according to the above embodiment can improve the drivability of aPMOSFET in a CMOSFET using a high-k gate insulating film.

Note that the above embodiment is merely an example and does not limitthe present invention. For example, it is also possible to form anN-type semiconductor region in the surface portion of a P-typesemiconductor substrate, and a P-type semiconductor region in thesurface portion of an N-type semiconductor substrate, instead of formingthe P-type semiconductor region 20 and N-type semiconductor region 30 inthe surface portion of the semiconductor substrate 10.

1. A semiconductor device fabrication method comprising: forming a firstgate electrode via a first gate insulating film on a P-typesemiconductor region formed in a surface portion of a semiconductorsubstrate, and forming a second gate electrode via a second gateinsulating film on an N-type semiconductor region formed in the surfaceportion of the semiconductor substrate; forming a first insulating filmon side surfaces of the first gate electrode and the first gateinsulating film, and forming a second insulating film on side surfacesof the second gate electrode and the second gate insulating film;forming a mask having a pattern corresponding to the P-typesemiconductor region; etching away the second insulating film by usingthe mask; removing the mask; and forming a first gate electrode sidewallinsulating film on the side surfaces of the first insulating film, andforming a second gate electrode sidewall insulating film on the sidesurfaces of the second gate electrode and the second gate insulatingfilm, thereby forming an interface insulating film in an interfacebetween the second gate electrode and the second gate insulating film.2. A method according to claim 1, further comprising, after the firstinsulating film and the second insulating film are formed,ion-implanting an N-type impurity into a surface portion of the P-typesemiconductor region by using the first gate electrode and the firstinsulating film as masks, thereby forming a first source region and afirst drain region, and ion-implanting a P-type impurity into a surfaceportion of the N-type semiconductor region by using the second gateelectrode and the second insulating film as masks, thereby forming asecond source region and a second drain region.
 3. A method according toclaim 1, further comprising, after the first gate electrode sidewallinsulating film and the second gate electrode sidewall insulating filmare formed, ion-implanting an N-type impurity into a surface portion ofthe P-type semiconductor region by using the first gate electrode, thefirst insulating film, and the first gate electrode sidewall insulatingfilm as masks, thereby forming a third source region and a third drainregion, and ion-implanting a P-type impurity into a surface portion ofthe N-type semiconductor region by using the second gate electrode andthe second gate electrode sidewall insulating film as masks, therebyforming a fourth source region and a fourth drain region.
 4. A methodaccording to claim 2, further comprising, after the first gate electrodesidewall insulating film and the second gate electrode sidewallinsulating film are formed, ion-implanting an N-type impurity into asurface portion of the P-type semiconductor region by using the firstgate electrode, the first insulating film, and the first gate electrodesidewall insulating film as masks, thereby forming a third source regionand a third drain region, and ion-implanting a P-type impurity into asurface portion of the N-type semiconductor region by using the secondgate electrode and the second gate electrode sidewall insulating film asmasks, thereby forming a fourth source region and a fourth drain region.5. A method according to claim 1, wherein each of the first gateinsulating film and the second gate insulating film is made of amaterial selected from the group consisting of a hafnium oxide film, azirconium oxide film, a silicate film of a hafnium oxide film, analuminate film of a hafnium oxide film, a silicate film of a zirconiumoxide film, an aluminate film of a zirconium oxide film, a silicatenitride film of a hafnium oxide film, an aluminate nitride film of ahafnium oxide film, a silicate nitride film of a zirconium oxide film,and an aluminate nitride film of a zirconium oxide film.
 6. A methodaccording to claim 2, wherein each of the first gate insulating film andthe second gate insulating film is made of a material selected from thegroup consisting of a hafnium oxide film, a zirconium oxide film, asilicate film of a hafnium oxide film, an aluminate film of a hafniumoxide film, a silicate film of a zirconium oxide film, an aluminate filmof a zirconium oxide film, a silicate nitride film of a hafnium oxidefilm, an aluminate nitride film of a hafnium oxide film, a silicatenitride film of a zirconium oxide film, and an aluminate nitride film ofa zirconium oxide film.
 7. A method according to claim 3, wherein eachof the first gate insulating film and the second gate insulating film ismade of a material selected from the group consisting of a hafnium oxidefilm, a zirconium oxide film, a silicate film of a hafnium oxide film,an aluminate film of a hafnium oxide film, a silicate film of azirconium oxide film, an aluminate film of a zirconium oxide film, asilicate nitride film of a hafnium oxide film, an aluminate nitride filmof a hafnium oxide film, a silicate nitride film of a zirconium oxidefilm, and an aluminate nitride film of a zirconium oxide film.
 8. Amethod according to claim 1, wherein the interface insulating film ismade of a silicon oxide film, and has a film thickness of 2 to 3 nm. 9.A method according to claim 2, wherein the interface insulating film ismade of a silicon oxide film, and has a film thickness of 2 to 3 nm. 10.A method according to claim 3, wherein the interface insulating film ismade of a silicon oxide film, and has a film thickness of 2 to 3 nm. 11.A method according to claim 1, wherein the first insulating film is madeof a silicon nitride film, and has a film thickness of about 2 nm.
 12. Amethod according to claim 2, wherein the first insulating film is madeof a silicon nitride film, and has a film thickness of about 2 nm.
 13. Amethod according to claim 3, wherein the first insulating film is madeof a silicon nitride film, and has a film thickness of about 2 nm.
 14. Asemiconductor device comprising: a first gate insulating film formed ona P-type semiconductor region in a surface portion of a semiconductorsubstrate; a first gate electrode formed on said first gate insulatingfilm; a first gate electrode sidewall insulating film formed on sidesurfaces of said first gate electrode and said first gate insulatingfilm via an insulating film; an N-channel transistor having a firstsource region and a first drain region formed on two sides of a firstchannel region formed in a surface portion of said P-type semiconductorregion below said first gate electrode; a second gate insulating filmformed on an N-type semiconductor region in the surface portion of saidsemiconductor substrate; a second gate electrode formed on said secondgate insulating film via an interface insulating film; a second gateelectrode sidewall insulating film formed on side surfaces of saidsecond gate electrode, said interface insulating film, and said secondgate insulating film; and a P-channel transistor having a second sourceregion and a second drain region formed on two sides of a second channelregion formed in a surface portion of said N-type semiconductor regionbelow said second gate electrode.
 15. A device according to claim 14,wherein each of said first gate insulating film and said second gateinsulating film is made of a material selected from the group consistingof a hafnium oxide film, a zirconium oxide film, a silicate film of ahafnium oxide film, an aluminate film of a hafnium oxide film, asilicate film of a zirconium oxide film, an aluminate film of azirconium oxide film, a silicate nitride film of a hafnium oxide film,an aluminate nitride film of a hafnium oxide film, a silicate nitridefilm of a zirconium oxide film, and an aluminate nitride film of azirconium oxide film.
 16. A device according to claim 14, wherein saidinterface insulating film is made of a silicon oxide film, and has afilm thickness of 2 to 3 nm.
 17. A device according to claim 14, whereinsaid insulating film is made of a silicon nitride film, and has a filmthickness of about 2 nm.